The fabrication of microelectronic components from a microelectronic workpiece, such as a semiconductor wafer substrate, polymer substrate, etc., involves a substantial number of processes. For purposes of the present application, a microelectronic workpiece is defined to include a workpiece formed from a substrate upon which microelectronic circuits or components, data storage elements or layers, and/or micro-mechanical elements are formed. There are a number of different processing operations performed on the microelectronic workpiece to fabricate the microelectronic component(s). Such operations include, for example, material deposition, patterning, doping, chemical mechanical polishing, electropolishing, and heat treatment.
Material deposition processing involves depositing or otherwise forming thin layers of material on the surface of the microelectronic workpiece (hereinafter described as, but not limited to, a semiconductor wafer). Patterning provides removal of selected portions of these added layers. Doping of the semiconductor wafer, or similar microelectronic workpiece, is the process of adding impurities known as “dopants” to the selected portions of the wafer to alter the electrical characteristics of the substrate material. Heat treatment of the semiconductor wafer involves heating and/or cooling the wafer to achieve specific process results. Chemical mechanical polishing involves the removal of material through a combined chemical/mechanical process while electropolishing involves the removal of material from a workpiece surface using electrochemical reactions.
Numerous processing devices, known as processing “tools”, have been developed to implement the foregoing processing operations. These tools take on different configurations depending on the type of workpiece used in the fabrication process and the process or processes executed by the tool. One tool configuration, known as the LT-210C™ processing tool and available from Semitool, Inc., of Kalispell, Mont., includes a plurality of microelectronic workpiece processing stations that utilize a workpiece holder and a process bowl or container for implementing wet processing operations. Such wet processing operations include electroplating, etching, cleaning, electroless deposition, electropolishing, etc. In connection with the present invention, it is the electrochemical processing stations used in the LT-210C™ that are noteworthy. Such electrochemical processing stations perform the foregoing electroplating, electropolishing, anodization, etc., of the microelectronic workpiece. It will be recognized that the electrochemical processing system set forth herein is readily adapted to implement each of the foregoing electrochemical processes.
In accordance with one configuration of the LT-210C™ tool, the electroplating stations include a workpiece holder and a process container that are disposed proximate one another. The workpiece holder and process container are operated to bring the microelectronic workpiece held by the workpiece holder into contact with an electroplating fluid disposed in the process container to form a processing chamber. Restricting the electroplating solution to the appropriate portions of the workpiece, however, is often problematic. Additionally, ensuring proper mass transfer conditions between the electroplating solution and the surface of the workpiece can be difficult. Absent such mass transfer control, the electrochemical processing of the workpiece surface can often be non-uniform. This can be particularly problematic in connection with the electroplating of metals. Still further, control of the shape and magnitude of the electric field is increasingly important.
Conventional electrochemical reactors have utilized various techniques to bring the electroplating solution into contact as with the surface of the workpiece in a controlled manner. For example, the electroplating solution may be brought into contact with the surface of the workpiece using partial or full immersion processing in which the electroplating solution resides in a processing container and at least one surface of the workpiece is brought into contact with or below the surface of the electroplating solution.
Electroplating and other electrochemical processes have become important in the production of semiconductor integrated circuits and other microelectronic devices from microelectronic workpieces. For example, electroplating is often used in the formation of one or more metal layers on the workpiece. These metal layers are often used to electrically interconnect the various devices of the integrated circuit. Further, the structures formed from the metal layers may constitute microelectronic devices such as read/write heads, etc.
Electroplated metals typically include copper, nickel, gold, platinum, solder, nickel-iron, etc. Electroplating is generally, effected by initial formation of a seed layer on the microelectronic workpiece in the form of a very thin layer of metal, whereby the surface of the microelectronic workpiece is rendered electrically conductive. This electro-conductivity permits subsequent formation of a blanket or patterned layer of the desired metal by electroplating. Subsequent processing, such as chemical mechanical planarization, may be used to remove unwanted portions of the patterned or metal blanket layer formed during electroplating, resulting in the formation of the desired metallized structure.
Electropolishing of metals at the surface of a workpiece involves the removal of at least some of the metal using an electrochemical process. The electrochemical process is effectively the reverse of the electroplating reaction and is often carried out using the same or similar reactors as electroplating.
Existing electroplating processing containers often provide a continuous flow of electroplating solution to the electroplating chamber through a single inlet disposed at the bottom portion of the chamber. One embodiment of such a processing container is illustrated in FIG. 1A. As illustrated, the electroplating reactor, shown generally at 1, includes a electroplating processing container 2 that is used to contain a flow of electroplating solution provided through a fluid inlet 3 disposed at a lower portion of the container 2. In such a reactor, the electroplating solution completes an electrical circuit path between an anode 4 and a surface of workpiece 5, which functions as a cathode.
The electroplating reactions that take place at the surface of the microelectronic workpiece are dependent on species mass transport (e.g., copper ions, platinum ions, gold ions, etc.) to the microelectronic workpiece surface through a diffusion layer (a.k.a. mass transport layer) that forms proximate the microelectronic workpiece's surface. It is desirable to have a diffusion layer that is both thin and uniform over the surface of the microelectronic workpiece if a uniform electroplated film is to be deposited within a reasonable amount of time.
Even distribution of the electroplating solution over the workpiece surface to control the thickness and uniformity of the diffusion layer in the processing container of FIG. 1A is facilitated, for example, by a diffuser 6 or the like that is disposed between the single inlet and the workpiece surface. The diffuser includes a plurality of apertures 7 that are provided to disburse the stream of electroplating fluid provided from the processing fluid inlet 3 as evenly as possible across the surface of the workpiece 5.
Although substantial improvements in diffusion layer control result from the use of a diffuser, such control is limited. With reference to FIG. 1A, localized areas 8 of increased flow velocity normal to the surface of the microelectronic workpiece are often generated by the diffuser 6. These localized areas generally correspond to the position of apertures 7 of the diffuser 6. This effect is increased as the diffuser 6 is moved closer to the workpiece.
The present inventors have found that these localized areas of increased flow velocity at the surface of the workpiece affect the diffusion layer conditions and can result in non-uniform deposition of the electroplated material over the surface of the workpiece. Diffuser hole pattern configurations also affect the distribution of the electric field since the diffuser is disposed between the anode and workpiece, and can result in non-uniform deposition of the electroplated material. In the reactor illustrated in FIG. 1A, the electric field tends to be concentrated at localized areas 8 corresponding to the apertures in the diffuser. These effects in the localized areas 8 are dependent on diffuser distance from the workpiece and the diffuser hole size and pattern.
Another problem often encountered in electroplating is disruption of the diffusion layer due to the entrapment and evolvement of gasses during the electroplating process. For example, bubbles can be created in the plumbing and pumping system of the processing equipment. Electroplating is thus inhibited at those sites on the surface of the workpiece to which the bubbles migrate. Gas evolvement is particularly a concern when an inert anode is utilized since inert anodes tend to generate gas bubbles as a result of the anodic reactions that take place at the anode's surface.
Consumable anodes are often used to reduce the evolvement of gas bubbles in the electroplating solution and to maintain bath stability. However, consumable anodes frequently have a passivated film surface that must be maintained. They also erode into the plating solution changing the dimensional tolerances. Ultimately, the) must be replaced thereby increasing the amount of maintenance required to keep the tool operational when compared to tools using inert anodes.
Another challenge associated with the plating of uniform films is the changing resistance of the plated film. The initial seed layer can have a high resistance and this resistance decreases as the film becomes thicker. The changing resistance makes it difficult for a given set of chamber hardware to yield optimal uniformity on a variety of seed layers and deposited film thicknesses.
In view of the foregoing, the present inventors have developed a system for electrochemically processing a microelectronic workpiece that can readily adapt to a wide range of electrochemical processing requirements (e.g., seed layer thicknesses, seed layer types, electroplating materials, electrolyte bath properties, etc.). The system can adapt to such electrochemical processing requirements while concurrently providing a controlled, substantially uniform diffusion layer at the surface of the workpiece that assists in providing a corresponding substantially uniform processing of the workpiece surface (e.g., uniform deposition of the electroplated material).